pgsql: logical decoding: fix decoding of a commit's commit time.

logical decoding: fix decoding of a commit's commit time.

When adding replication origins in 5aa235042, I somehow managed to set
the timestamp of decoded transactions to InvalidXLogRecptr when decoding
one made without a replication origin. Fix that, and the wrong type of
the new commit_time variable.

This didn't trigger a regression test failure because we explicitly
don't show commit timestamps in the regression tests, as they obviously
are variable. Add a test that checks that a decoded commit's timestamp
is within minutes of NOW() from before the commit.

Reported-By: Weiping Qu
Diagnosed-By: Artur Zakirov
Discussion: 56D4197E.9050706@informatik.uni-kl.de,
    56D42918.1010108@postgrespro.ru
Backpatch: 9.5, where 5aa235042 originates.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/7c17aac69dcae610b08c5965161151cd282f16bc

Modified Files
--------------
contrib/test_decoding/Makefile           |  2 +-
contrib/test_decoding/expected/time.out  | 40 ++++++++++++++++++++++++++++++++
contrib/test_decoding/sql/time.sql       | 22 ++++++++++++++++++
src/backend/replication/logical/decode.c |  2 +-
4 files changed, 64 insertions(+), 2 deletions(-)